feat: allow approved external MCP tools in root plan mode (#24509)

## Summary

Allow root plan-mode chats to use MCP tools from external servers that
an admin has explicitly approved for plan mode. Workspace MCP and
plan-mode subagents remain blocked.

## Problem

`chatd.go` excluded every MCP tool when `isPlanModeTurn` was true, so
planning had no access to tools like docs search, ticketing, etc.
Lifting that guard wholesale was unsafe: `mcp_server_configs` already
has centralized admin governance, but workspace-local MCP (discovered
from agent `.mcp.json`) does not, and subagents use a narrower trust
boundary.

## Fix

Add an admin-controlled per-server `allow_in_plan_mode` flag (default
`false`) and gate plan-mode MCP access on it.

### Backend / schema
- New migration `000472_mcp_server_allow_in_plan_mode.{up,down}.sql` and
matching fixture update.
- `mcpserverconfigs.sql` + generated code: persist and read the new
column.
- `codersdk/mcp.go`: thread the field through `MCPServerConfig`,
`Create*`, and `Update*` request types.
- `coderd/mcp.go`: validate, persist, and return the flag in
get/list/create/update handlers.

### chatd
- `coderd/x/chatd/chatd.go`: pre-filter selected external MCP configs by
`AllowInPlanMode` before calling `mcpclient.ConnectAll` on plan-mode
root turns. Workspace MCP discovery is skipped entirely on plan-mode
turns.
- Single helper decides whether a tool is available in plan mode, used
both at construction and for active-tool filtering (defense in depth).
Plan-mode subagents, dynamic tools, provider-native tools, computer-use,
and workspace MCP stay unchanged.
- `coderd/x/chatd/prompt.go`: update the root plan-mode overlay text to
match the new boundary.

### UI
- `MCPServerAdminPanel.tsx`: add an explicit toggle ("Allow all tools
from this MCP server in root plan mode") next to the existing governance
controls.
- Regenerated `site/src/api/typesGenerated.ts`.

### Docs
- `docs/ai-coder/agents/architecture.md`: replace the blanket "MCP is
unavailable in plan mode" note with the new root-only, external-only,
admin-approved policy. Explicitly call out that workspace MCP and
plan-mode subagents are still excluded.

### Tests
- Plan-mode visibility (approved vs non-approved external server).
- Plan-mode invocation of an approved external MCP tool.
- End-to-end plan-mode workflow that uses an approved MCP tool and then
reaches `propose_plan`.
- Regressions: workspace MCP still excluded in plan mode; plan-mode
subagents still on the restricted tool boundary; existing tool
allow/deny list filtering still applies.

## Policy precedence

`allow_in_plan_mode` is an **additional** requirement on top of existing
`enabled`, availability, chat-selected / forced server IDs, and tool
allow/deny lists. It approves **all tools on that server** for root plan
mode; a per-tool plan allowlist is deliberately deferred.

## Follow-ups (explicitly out of scope)

- Whether plan-mode subagents should inherit approved external MCP
tools.
- Workspace-local MCP safety model (agent-side `.mcp.json` schema vs. a
coderd-managed workspace MCP config).

## Validation

- `go vet ./coderd/x/chatd/...`
- `go test ./coderd/x/chatd -run 'TestPlan.*|TestMCP.*' -count=1`
- `go test ./coderd/x/chatd -count=1 -timeout 5m` (full chatd suite)
- `make fmt` (no diff)

> Mux opened this PR on Mike's behalf.

coderd/database/dump.sql

@@ -1788,6 +1788,7 @@ CREATE TABLE mcp_server_configs (
     created_at timestamp with time zone DEFAULT now() NOT NULL,
     updated_at timestamp with time zone DEFAULT now() NOT NULL,
     model_intent boolean DEFAULT false NOT NULL,
+    allow_in_plan_mode boolean DEFAULT false NOT NULL,
     CONSTRAINT mcp_server_configs_auth_type_check CHECK ((auth_type = ANY (ARRAY['none'::text, 'oauth2'::text, 'api_key'::text, 'custom_headers'::text]))),
     CONSTRAINT mcp_server_configs_availability_check CHECK ((availability = ANY (ARRAY['force_on'::text, 'default_on'::text, 'default_off'::text]))),
     CONSTRAINT mcp_server_configs_transport_check CHECK ((transport = ANY (ARRAY['streamable_http'::text, 'sse'::text])))

coderd/database/migrations/000472_mcp_server_allow_in_plan_mode.down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE mcp_server_configs
+    DROP COLUMN allow_in_plan_mode;

coderd/database/migrations/000472_mcp_server_allow_in_plan_mode.up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE mcp_server_configs
+    ADD COLUMN allow_in_plan_mode BOOLEAN NOT NULL DEFAULT false;

coderd/database/migrations/testdata/fixtures/000472_mcp_server_allow_in_plan_mode.up.sql

@@ -0,0 +1,6 @@
+-- Migration 472 adds allow_in_plan_mode with a default of false.
+-- Flip the existing fixture row to true here so fixture data exercises
+-- the non-default state only after the column exists.
+UPDATE mcp_server_configs
+SET allow_in_plan_mode = TRUE
+WHERE id = 'a1b2c3d4-e5f6-7890-abcd-ef1234567890';

coderd/database/models.go

@@ -4729,6 +4729,7 @@ type MCPServerConfig struct {
 	CreatedAt               time.Time      `db:"created_at" json:"created_at"`
 	UpdatedAt               time.Time      `db:"updated_at" json:"updated_at"`
 	ModelIntent             bool           `db:"model_intent" json:"model_intent"`
+	AllowInPlanMode         bool           `db:"allow_in_plan_mode" json:"allow_in_plan_mode"`
 }
 
 type MCPServerUserToken struct {

coderd/database/queries.sql.go

@@ -12764,7 +12764,7 @@ func (q *sqlQuerier) DeleteMCPServerUserToken(ctx context.Context, arg DeleteMCP
 
 const getEnabledMCPServerConfigs = `-- name: GetEnabledMCPServerConfigs :many
 SELECT
-    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent
+    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent, allow_in_plan_mode
 FROM
     mcp_server_configs
 WHERE
@@ -12811,6 +12811,7 @@ func (q *sqlQuerier) GetEnabledMCPServerConfigs(ctx context.Context) ([]MCPServe
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.ModelIntent,
+			&i.AllowInPlanMode,
 		); err != nil {
 			return nil, err
 		}
@@ -12827,7 +12828,7 @@ func (q *sqlQuerier) GetEnabledMCPServerConfigs(ctx context.Context) ([]MCPServe
 
 const getForcedMCPServerConfigs = `-- name: GetForcedMCPServerConfigs :many
 SELECT
-    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent
+    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent, allow_in_plan_mode
 FROM
     mcp_server_configs
 WHERE
@@ -12875,6 +12876,7 @@ func (q *sqlQuerier) GetForcedMCPServerConfigs(ctx context.Context) ([]MCPServer
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.ModelIntent,
+			&i.AllowInPlanMode,
 		); err != nil {
 			return nil, err
 		}
@@ -12891,7 +12893,7 @@ func (q *sqlQuerier) GetForcedMCPServerConfigs(ctx context.Context) ([]MCPServer
 
 const getMCPServerConfigByID = `-- name: GetMCPServerConfigByID :one
 SELECT
-    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent
+    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent, allow_in_plan_mode
 FROM
     mcp_server_configs
 WHERE
@@ -12930,13 +12932,14 @@ func (q *sqlQuerier) GetMCPServerConfigByID(ctx context.Context, id uuid.UUID) (
 		&i.CreatedAt,
 		&i.UpdatedAt,
 		&i.ModelIntent,
+		&i.AllowInPlanMode,
 	)
 	return i, err
 }
 
 const getMCPServerConfigBySlug = `-- name: GetMCPServerConfigBySlug :one
 SELECT
-    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent
+    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent, allow_in_plan_mode
 FROM
     mcp_server_configs
 WHERE
@@ -12975,13 +12978,14 @@ func (q *sqlQuerier) GetMCPServerConfigBySlug(ctx context.Context, slug string)
 		&i.CreatedAt,
 		&i.UpdatedAt,
 		&i.ModelIntent,
+		&i.AllowInPlanMode,
 	)
 	return i, err
 }
 
 const getMCPServerConfigs = `-- name: GetMCPServerConfigs :many
 SELECT
-    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent
+    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent, allow_in_plan_mode
 FROM
     mcp_server_configs
 ORDER BY
@@ -13026,6 +13030,7 @@ func (q *sqlQuerier) GetMCPServerConfigs(ctx context.Context) ([]MCPServerConfig
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.ModelIntent,
+			&i.AllowInPlanMode,
 		); err != nil {
 			return nil, err
 		}
@@ -13042,7 +13047,7 @@ func (q *sqlQuerier) GetMCPServerConfigs(ctx context.Context) ([]MCPServerConfig
 
 const getMCPServerConfigsByIDs = `-- name: GetMCPServerConfigsByIDs :many
 SELECT
-    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent
+    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent, allow_in_plan_mode
 FROM
     mcp_server_configs
 WHERE
@@ -13089,6 +13094,7 @@ func (q *sqlQuerier) GetMCPServerConfigsByIDs(ctx context.Context, ids []uuid.UU
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.ModelIntent,
+			&i.AllowInPlanMode,
 		); err != nil {
 			return nil, err
 		}
@@ -13206,6 +13212,7 @@ INSERT INTO mcp_server_configs (
     availability,
     enabled,
     model_intent,
+    allow_in_plan_mode,
     created_by,
     updated_by
 ) VALUES (
@@ -13232,11 +13239,12 @@ INSERT INTO mcp_server_configs (
     $21::text,
     $22::boolean,
     $23::boolean,
-    $24::uuid,
-    $25::uuid
+    $24::boolean,
+    $25::uuid,
+    $26::uuid
 )
 RETURNING
-    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent
+    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent, allow_in_plan_mode
 `
 
 type InsertMCPServerConfigParams struct {
@@ -13263,6 +13271,7 @@ type InsertMCPServerConfigParams struct {
 	Availability            string         `db:"availability" json:"availability"`
 	Enabled                 bool           `db:"enabled" json:"enabled"`
 	ModelIntent             bool           `db:"model_intent" json:"model_intent"`
+	AllowInPlanMode         bool           `db:"allow_in_plan_mode" json:"allow_in_plan_mode"`
 	CreatedBy               uuid.UUID      `db:"created_by" json:"created_by"`
 	UpdatedBy               uuid.UUID      `db:"updated_by" json:"updated_by"`
 }
@@ -13292,6 +13301,7 @@ func (q *sqlQuerier) InsertMCPServerConfig(ctx context.Context, arg InsertMCPSer
 		arg.Availability,
 		arg.Enabled,
 		arg.ModelIntent,
+		arg.AllowInPlanMode,
 		arg.CreatedBy,
 		arg.UpdatedBy,
 	)
@@ -13325,6 +13335,7 @@ func (q *sqlQuerier) InsertMCPServerConfig(ctx context.Context, arg InsertMCPSer
 		&i.CreatedAt,
 		&i.UpdatedAt,
 		&i.ModelIntent,
+		&i.AllowInPlanMode,
 	)
 	return i, err
 }
@@ -13356,12 +13367,13 @@ SET
     availability = $21::text,
     enabled = $22::boolean,
     model_intent = $23::boolean,
-    updated_by = $24::uuid,
+    allow_in_plan_mode = $24::boolean,
+    updated_by = $25::uuid,
     updated_at = NOW()
 WHERE
-    id = $25::uuid
+    id = $26::uuid
 RETURNING
-    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent
+    id, display_name, slug, description, icon_url, transport, url, auth_type, oauth2_client_id, oauth2_client_secret, oauth2_client_secret_key_id, oauth2_auth_url, oauth2_token_url, oauth2_scopes, api_key_header, api_key_value, api_key_value_key_id, custom_headers, custom_headers_key_id, tool_allow_list, tool_deny_list, availability, enabled, created_by, updated_by, created_at, updated_at, model_intent, allow_in_plan_mode
 `
 
 type UpdateMCPServerConfigParams struct {
@@ -13388,6 +13400,7 @@ type UpdateMCPServerConfigParams struct {
 	Availability            string         `db:"availability" json:"availability"`
 	Enabled                 bool           `db:"enabled" json:"enabled"`
 	ModelIntent             bool           `db:"model_intent" json:"model_intent"`
+	AllowInPlanMode         bool           `db:"allow_in_plan_mode" json:"allow_in_plan_mode"`
 	UpdatedBy               uuid.UUID      `db:"updated_by" json:"updated_by"`
 	ID                      uuid.UUID      `db:"id" json:"id"`
 }
@@ -13417,6 +13430,7 @@ func (q *sqlQuerier) UpdateMCPServerConfig(ctx context.Context, arg UpdateMCPSer
 		arg.Availability,
 		arg.Enabled,
 		arg.ModelIntent,
+		arg.AllowInPlanMode,
 		arg.UpdatedBy,
 		arg.ID,
 	)
@@ -13450,6 +13464,7 @@ func (q *sqlQuerier) UpdateMCPServerConfig(ctx context.Context, arg UpdateMCPSer
 		&i.CreatedAt,
 		&i.UpdatedAt,
 		&i.ModelIntent,
+		&i.AllowInPlanMode,
 	)
 	return i, err
 }

coderd/database/queries/mcpserverconfigs.sql

@@ -78,6 +78,7 @@ INSERT INTO mcp_server_configs (
     availability,
     enabled,
     model_intent,
+    allow_in_plan_mode,
     created_by,
     updated_by
 ) VALUES (
@@ -104,6 +105,7 @@ INSERT INTO mcp_server_configs (
     @availability::text,
     @enabled::boolean,
     @model_intent::boolean,
+    @allow_in_plan_mode::boolean,
     @created_by::uuid,
     @updated_by::uuid
 )
@@ -137,6 +139,7 @@ SET
     availability = @availability::text,
     enabled = @enabled::boolean,
     model_intent = @model_intent::boolean,
+    allow_in_plan_mode = @allow_in_plan_mode::boolean,
     updated_by = @updated_by::uuid,
     updated_at = NOW()
 WHERE

coderd/mcp.go

@@ -171,6 +171,7 @@ func (api *API) createMCPServerConfig(rw http.ResponseWriter, r *http.Request) {
 				Availability:            strings.TrimSpace(req.Availability),
 				Enabled:                 req.Enabled,
 				ModelIntent:             req.ModelIntent,
+				AllowInPlanMode:         req.AllowInPlanMode,
 				CreatedBy:               apiKey.UserID,
 				UpdatedBy:               apiKey.UserID,
 			})
@@ -258,6 +259,7 @@ func (api *API) createMCPServerConfig(rw http.ResponseWriter, r *http.Request) {
 				Availability:            inserted.Availability,
 				Enabled:                 inserted.Enabled,
 				ModelIntent:             inserted.ModelIntent,
+				AllowInPlanMode:         inserted.AllowInPlanMode,
 				UpdatedBy:               apiKey.UserID,
 			})
 			if err != nil {
@@ -326,6 +328,7 @@ func (api *API) createMCPServerConfig(rw http.ResponseWriter, r *http.Request) {
 		Availability:            strings.TrimSpace(req.Availability),
 		Enabled:                 req.Enabled,
 		ModelIntent:             req.ModelIntent,
+		AllowInPlanMode:         req.AllowInPlanMode,
 		CreatedBy:               apiKey.UserID,
 		UpdatedBy:               apiKey.UserID,
 	})
@@ -580,6 +583,11 @@ func (api *API) updateMCPServerConfig(rw http.ResponseWriter, r *http.Request) {
 			modelIntent = *req.ModelIntent
 		}
 
+		allowInPlanMode := existing.AllowInPlanMode
+		if req.AllowInPlanMode != nil {
+			allowInPlanMode = *req.AllowInPlanMode
+		}
+
 		// When auth_type changes, clear fields belonging to the
 		// previous auth type so stale secrets don't persist.
 		if authType != existing.AuthType {
@@ -648,6 +656,7 @@ func (api *API) updateMCPServerConfig(rw http.ResponseWriter, r *http.Request) {
 			Availability:            availability,
 			Enabled:                 enabled,
 			ModelIntent:             modelIntent,
+			AllowInPlanMode:         allowInPlanMode,
 			UpdatedBy:               apiKey.UserID,
 			ID:                      existing.ID,
 		})
@@ -1129,10 +1138,11 @@ func convertMCPServerConfig(config database.MCPServerConfig) codersdk.MCPServerC
 
 		Availability: config.Availability,
 
-		Enabled:     config.Enabled,
-		ModelIntent: config.ModelIntent,
-		CreatedAt:   config.CreatedAt,
-		UpdatedAt:   config.UpdatedAt,
+		Enabled:         config.Enabled,
+		ModelIntent:     config.ModelIntent,
+		AllowInPlanMode: config.AllowInPlanMode,
+		CreatedAt:       config.CreatedAt,
+		UpdatedAt:       config.UpdatedAt,
 	}
 }
 

coderd/mcp_test.go

@@ -100,37 +100,52 @@ func TestMCPServerConfigsCRUD(t *testing.T) {
 	require.Equal(t, "client-id-123", created.OAuth2ClientID)
 	require.Equal(t, "default_on", created.Availability)
 	require.True(t, created.Enabled)
+	require.False(t, created.AllowInPlanMode)
 
 	// Verify the secret is indicated but never returned.
 	require.True(t, created.HasOAuth2Secret)
 
-	// Verify the config appears in the list.
+	// Verify the config appears in the list and direct get responses.
 	configs, err := client.MCPServerConfigs(ctx)
 	require.NoError(t, err)
 	require.Len(t, configs, 1)
 	require.Equal(t, created.ID, configs[0].ID)
 	require.True(t, configs[0].HasOAuth2Secret)
+	require.False(t, configs[0].AllowInPlanMode)
 
-	// Update display name and availability.
+	fetched, err := client.MCPServerConfigByID(ctx, created.ID)
+	require.NoError(t, err)
+	require.Equal(t, created.ID, fetched.ID)
+	require.False(t, fetched.AllowInPlanMode)
+
+	// Update display name, availability, and allow_in_plan_mode.
 	newName := "Renamed Server"
 	newAvail := "force_on"
+	allowInPlanMode := true
 	updated, err := client.UpdateMCPServerConfig(ctx, created.ID, codersdk.UpdateMCPServerConfigRequest{
-		DisplayName:  &newName,
-		Availability: &newAvail,
+		DisplayName:     &newName,
+		Availability:    &newAvail,
+		AllowInPlanMode: &allowInPlanMode,
 	})
 	require.NoError(t, err)
 	require.Equal(t, "Renamed Server", updated.DisplayName)
 	require.Equal(t, "force_on", updated.Availability)
+	require.True(t, updated.AllowInPlanMode)
 	// Unchanged fields should remain the same.
 	require.Equal(t, "my-mcp-server", updated.Slug)
 	require.Equal(t, "oauth2", updated.AuthType)
 
-	// Verify the update took effect through the list.
+	// Verify the update took effect through the list and direct get.
 	configs, err = client.MCPServerConfigs(ctx)
 	require.NoError(t, err)
 	require.Len(t, configs, 1)
 	require.Equal(t, "Renamed Server", configs[0].DisplayName)
 	require.Equal(t, "force_on", configs[0].Availability)
+	require.True(t, configs[0].AllowInPlanMode)
+
+	fetched, err = client.MCPServerConfigByID(ctx, created.ID)
+	require.NoError(t, err)
+	require.True(t, fetched.AllowInPlanMode)
 
 	// Delete it.
 	err = client.DeleteMCPServerConfig(ctx, created.ID)

coderd/x/chatd/chatd.go

@@ -5148,40 +5148,99 @@ func isExploreSubagentMode(mode database.NullChatMode) bool {
 	return mode.Valid && mode.ChatMode == database.ChatModeExplore
 }
 
-func allowedPlanToolNames(
-	allTools []fantasy.AgentTool,
+func filterExternalMCPConfigsForTurn(
+	configs []database.MCPServerConfig,
+	mode database.NullChatPlanMode,
 	parentChatID uuid.NullUUID,
-) []string {
-	isRootChat := !parentChatID.Valid
-	builtinPlanPolicy := map[string]bool{
-		"read_file":                true,
-		"write_file":               isRootChat,
-		"edit_files":               isRootChat,
-		"execute":                  true,
-		"process_output":           true,
-		"process_list":             false,
-		"process_signal":           false,
-		"list_templates":           isRootChat,
-		"read_template":            isRootChat,
-		"create_workspace":         isRootChat,
-		"start_workspace":          isRootChat,
-		"propose_plan":             isRootChat,
-		"spawn_agent":              isRootChat,
-		"spawn_explore_agent":      isRootChat,
-		"wait_agent":               isRootChat,
-		"message_agent":            false,
-		"close_agent":              false,
-		"spawn_computer_use_agent": false,
-		"read_skill":               true,
-		"read_skill_file":          true,
-		"ask_user_question":        isRootChat,
+) ([]database.MCPServerConfig, map[uuid.UUID]struct{}) {
+	if !mode.Valid || mode.ChatPlanMode != database.ChatPlanModePlan {
+		return configs, nil
+	}
+	if parentChatID.Valid {
+		// Plan-mode subagents do not receive external MCP tools because
+		// their trust boundary is narrower than the root chat's.
+		return nil, map[uuid.UUID]struct{}{}
 	}
 
+	filtered := make([]database.MCPServerConfig, 0, len(configs))
+	approvedIDs := make(map[uuid.UUID]struct{})
+	for _, cfg := range configs {
+		if !cfg.AllowInPlanMode {
+			continue
+		}
+		filtered = append(filtered, cfg)
+		approvedIDs[cfg.ID] = struct{}{}
+	}
+	return filtered, approvedIDs
+}
+
+func builtinPlanToolAllowed(name string, isRootChat bool) bool {
+	switch name {
+	case "read_file", "execute", "process_output", "read_skill", "read_skill_file":
+		return true
+	case "write_file", "edit_files", "list_templates", "read_template",
+		"create_workspace", "start_workspace", "propose_plan", "spawn_agent",
+		"spawn_explore_agent", "wait_agent", "ask_user_question":
+		return isRootChat
+	case "process_list", "process_signal", "message_agent", "close_agent",
+		"spawn_computer_use_agent":
+		return false
+	default:
+		return false
+	}
+}
+
+func toolAllowedForTurn(
+	tool fantasy.AgentTool,
+	mode database.NullChatPlanMode,
+	parentChatID uuid.NullUUID,
+	approvedMCPConfigIDs map[uuid.UUID]struct{},
+) bool {
+	if !mode.Valid || mode.ChatPlanMode != database.ChatPlanModePlan {
+		return true
+	}
+	if builtinPlanToolAllowed(tool.Info().Name, !parentChatID.Valid) {
+		return true
+	}
+	mcpTool, ok := tool.(mcpclient.MCPToolIdentifier)
+	if !ok {
+		return false
+	}
+	_, approved := approvedMCPConfigIDs[mcpTool.MCPServerConfigID()]
+	return approved
+}
+
+func filterToolsForTurn(
+	allTools []fantasy.AgentTool,
+	mode database.NullChatPlanMode,
+	parentChatID uuid.NullUUID,
+	approvedMCPConfigIDs map[uuid.UUID]struct{},
+) []fantasy.AgentTool {
+	if !mode.Valid || mode.ChatPlanMode != database.ChatPlanModePlan {
+		return allTools
+	}
+
+	filtered := make([]fantasy.AgentTool, 0, len(allTools))
+	for _, tool := range allTools {
+		if toolAllowedForTurn(tool, mode, parentChatID, approvedMCPConfigIDs) {
+			filtered = append(filtered, tool)
+		}
+	}
+	return filtered
+}
+
+// activeToolNamesForTurn extends the built-in plan allowlist with approved
+// external MCP tools for root plan-mode chats.
+func activeToolNamesForTurn(
+	allTools []fantasy.AgentTool,
+	mode database.NullChatPlanMode,
+	parentChatID uuid.NullUUID,
+	approvedMCPConfigIDs map[uuid.UUID]struct{},
+) []string {
 	toolNames := make([]string, 0, len(allTools))
 	for _, tool := range allTools {
-		name := tool.Info().Name
-		if builtinPlanPolicy[name] {
-			toolNames = append(toolNames, name)
+		if toolAllowedForTurn(tool, mode, parentChatID, approvedMCPConfigIDs) {
+			toolNames = append(toolNames, tool.Info().Name)
 		}
 	}
 	return toolNames
@@ -5222,30 +5281,24 @@ func allowedExploreToolNames(allTools []fantasy.AgentTool) []string {
 	return toolNames
 }
 
-// allowedBehaviorToolNames applies behavior-specific precedence for
-// tool filtering: Explore mode wins over plan mode, and plan mode wins
-// over the default behavior that allows all tools.
+// allowedBehaviorToolNames runs only on non-plan turns because
+// appendDynamicTools returns early for plan mode. Within that boundary,
+// Explore mode wins over the default behavior that allows all tools.
 func allowedBehaviorToolNames(
 	allTools []fantasy.AgentTool,
-	planMode database.NullChatPlanMode,
 	chatMode database.NullChatMode,
-	parentChatID uuid.NullUUID,
 ) []string {
 	if isExploreSubagentMode(chatMode) {
 		return allowedExploreToolNames(allTools)
 	}
-	if planMode.Valid && planMode.ChatPlanMode == database.ChatPlanModePlan {
-		return allowedPlanToolNames(allTools, parentChatID)
-	}
 	return allToolNames(allTools)
 }
 
-func stopAfterBehaviorTools(
+func stopAfterPlanTools(
 	planMode database.NullChatPlanMode,
-	chatMode database.NullChatMode,
 	parentChatID uuid.NullUUID,
 ) map[string]struct{} {
-	if isExploreSubagentMode(chatMode) || !planMode.Valid || planMode.ChatPlanMode != database.ChatPlanModePlan {
+	if !planMode.Valid || planMode.ChatPlanMode != database.ChatPlanModePlan {
 		return nil
 	}
 	stopTools := map[string]struct{}{
@@ -5257,6 +5310,17 @@ func stopAfterBehaviorTools(
 	return stopTools
 }
 
+func stopAfterBehaviorTools(
+	planMode database.NullChatPlanMode,
+	chatMode database.NullChatMode,
+	parentChatID uuid.NullUUID,
+) map[string]struct{} {
+	if isExploreSubagentMode(chatMode) {
+		return nil
+	}
+	return stopAfterPlanTools(planMode, parentChatID)
+}
+
 type systemPromptBehaviorContext struct {
 	planMode             database.NullChatPlanMode
 	chatMode             database.NullChatMode
@@ -5432,7 +5496,6 @@ func appendDynamicTools(
 	raw pqtype.NullRawMessage,
 	planMode database.NullChatPlanMode,
 	chatMode database.NullChatMode,
-	parentChatID uuid.NullUUID,
 ) ([]fantasy.AgentTool, map[string]bool, error) {
 	if isExploreSubagentMode(chatMode) || (planMode.Valid && planMode.ChatPlanMode == database.ChatPlanModePlan) {
 		return tools, nil, nil
@@ -5454,7 +5517,7 @@ func appendDynamicTools(
 	}
 
 	activeToolNames := make(map[string]struct{}, len(tools))
-	for _, name := range allowedBehaviorToolNames(tools, planMode, chatMode, parentChatID) {
+	for _, name := range allowedBehaviorToolNames(tools, chatMode) {
 		activeToolNames[name] = struct{}{}
 	}
 	for _, t := range tools {
@@ -5569,6 +5632,12 @@ func (p *Server) runChat(
 	currentPlanMode := chat.PlanMode
 	isPlanModeTurn := currentPlanMode.Valid && currentPlanMode.ChatPlanMode == database.ChatPlanModePlan
 	isExploreSubagent := isExploreSubagentMode(chat.Mode)
+	isRootChat := !chat.ParentChatID.Valid
+	mcpConnectConfigs, approvedPlanMCPConfigIDs := filterExternalMCPConfigsForTurn(
+		mcpConfigs,
+		currentPlanMode,
+		chat.ParentChatID,
+	)
 	planModeInstructions := p.loadPlanModeInstructions(ctx, currentPlanMode, logger)
 
 	chainInfo := resolveChainMode(messages)
@@ -5767,17 +5836,20 @@ func (p *Server) runChat(
 		resolvedUserPrompt = p.resolveUserPrompt(ctx, chat.OwnerID)
 		return nil
 	})
-	if len(mcpConfigs) > 0 {
+	if len(mcpConnectConfigs) > 0 {
 		g2.Go(func() error {
 			// Refresh expired OAuth2 tokens before connecting.
-			mcpTokens = p.refreshExpiredMCPTokens(ctx, logger, mcpConfigs, mcpTokens)
+			mcpTokens = p.refreshExpiredMCPTokens(ctx, logger, mcpConnectConfigs, mcpTokens)
 			mcpTools, mcpCleanup = mcpclient.ConnectAll(
-				ctx, logger, mcpConfigs, mcpTokens,
+				ctx, logger, mcpConnectConfigs, mcpTokens,
 			)
 			return nil
 		})
 	}
-	if chat.WorkspaceID.Valid {
+	// Workspace MCP discovery stays disabled for all plan-mode turns.
+	// Root plan mode only gets approved external MCP servers, and
+	// plan-mode subagents get no MCP tools.
+	if chat.WorkspaceID.Valid && !isPlanModeTurn {
 		g2.Go(func() error {
 			// Fast path: check cache using the in-memory cached
 			// agent (ensureWorkspaceAgent is free when already
@@ -5848,7 +5920,6 @@ func (p *Server) runChat(
 	if err := g2.Wait(); err != nil {
 		return result, err
 	}
-	isRootChat := !chat.ParentChatID.Valid
 	subagentInstruction := ""
 	if !isRootChat {
 		subagentInstruction = defaultSubagentInstruction
@@ -6280,13 +6351,22 @@ func (p *Server) runChat(
 		builtinToolNames[t.Info().Name] = true
 	}
 
-	// Append tools from external MCP servers. These appear
-	// after the built-in tools so the LLM sees them as
-	// additional capabilities.
-	if !isPlanModeTurn && !isExploreSubagent {
+	// Append external and workspace MCP tools after the built-ins so the
+	// LLM sees them as additional capabilities. Explore subagents keep
+	// the narrower built-in-only boundary from main. Root plan mode gets
+	// only approved external MCP tools because mcpConnectConfigs was
+	// pre-filtered above, and filterToolsForTurn removes any remaining
+	// plan-mode ineligible tools from the assembled set.
+	if !isExploreSubagent {
 		tools = append(tools, mcpTools...)
 		tools = append(tools, workspaceMCPTools...)
 	}
+	tools = filterToolsForTurn(
+		tools,
+		currentPlanMode,
+		chat.ParentChatID,
+		approvedPlanMCPConfigIDs,
+	)
 	// Append dynamic tools declared by the client at chat
 	// creation time. These appear in the LLM's tool list but
 	// are never executed by the chatloop. The client handles
@@ -6299,7 +6379,6 @@ func (p *Server) runChat(
 		chat.DynamicTools,
 		currentPlanMode,
 		chat.Mode,
-		chat.ParentChatID,
 	)
 	if err != nil {
 		return result, err
@@ -6351,6 +6430,16 @@ func (p *Server) runChat(
 		)
 		prompt = filterPromptForChainMode(prompt, chainInfo)
 	}
+	activeToolNames := activeToolNamesForTurn(
+		tools,
+		currentPlanMode,
+		chat.ParentChatID,
+		approvedPlanMCPConfigIDs,
+	)
+	if isExploreSubagent {
+		activeToolNames = allowedExploreToolNames(tools)
+	}
+
 	var loopErr error
 	triggerMessageID, historyTipMessageID, triggerLabel := deriveChatDebugSeed(messages)
 	result.TriggerMessageID = triggerMessageID
@@ -6382,7 +6471,7 @@ func (p *Server) runChat(
 		Model:            model,
 		Messages:         prompt,
 		Tools:            tools,
-		ActiveTools:      allowedBehaviorToolNames(tools, currentPlanMode, chat.Mode, chat.ParentChatID),
+		ActiveTools:      activeToolNames,
 		StopAfterTools:   stopAfterBehaviorTools(currentPlanMode, chat.Mode, chat.ParentChatID),
 		MaxSteps:         maxChatSteps,
 		Metrics:          p.metrics,

coderd/x/chatd/chatd_internal_test.go

@@ -59,7 +59,75 @@ func (t *testAgentTool) SetProviderOptions(opts fantasy.ProviderOptions) {
 	t.providerOptions = opts
 }
 
-func TestAllowedPlanToolNames(t *testing.T) {
+type testMCPAgentTool struct {
+	*testAgentTool
+	configID uuid.UUID
+}
+
+func newTestMCPAgentTool(name string, configID uuid.UUID) fantasy.AgentTool {
+	return &testMCPAgentTool{
+		testAgentTool: &testAgentTool{info: fantasy.ToolInfo{Name: name}},
+		configID:      configID,
+	}
+}
+
+func (t *testMCPAgentTool) MCPServerConfigID() uuid.UUID {
+	return t.configID
+}
+
+func TestFilterExternalMCPConfigsForTurn(t *testing.T) {
+	t.Parallel()
+
+	approvedConfig := database.MCPServerConfig{ID: uuid.New(), AllowInPlanMode: true}
+	blockedConfig := database.MCPServerConfig{ID: uuid.New(), AllowInPlanMode: false}
+	configs := []database.MCPServerConfig{approvedConfig, blockedConfig}
+	planMode := database.NullChatPlanMode{
+		ChatPlanMode: database.ChatPlanModePlan,
+		Valid:        true,
+	}
+
+	t.Run("NonPlanModePassesThroughAllConfigs", func(t *testing.T) {
+		t.Parallel()
+
+		filtered, approvedIDs := filterExternalMCPConfigsForTurn(
+			configs,
+			database.NullChatPlanMode{},
+			uuid.NullUUID{},
+		)
+
+		require.Equal(t, configs, filtered)
+		require.Nil(t, approvedIDs)
+	})
+
+	t.Run("PlanModeSubagentsReturnNoConfigs", func(t *testing.T) {
+		t.Parallel()
+
+		filtered, approvedIDs := filterExternalMCPConfigsForTurn(
+			configs,
+			planMode,
+			uuid.NullUUID{UUID: uuid.New(), Valid: true},
+		)
+
+		require.Nil(t, filtered)
+		require.NotNil(t, approvedIDs)
+		require.Empty(t, approvedIDs)
+	})
+
+	t.Run("PlanModeRootFiltersToApprovedConfigs", func(t *testing.T) {
+		t.Parallel()
+
+		filtered, approvedIDs := filterExternalMCPConfigsForTurn(
+			configs,
+			planMode,
+			uuid.NullUUID{},
+		)
+
+		require.Equal(t, []database.MCPServerConfig{approvedConfig}, filtered)
+		require.Equal(t, map[uuid.UUID]struct{}{approvedConfig.ID: {}}, approvedIDs)
+	})
+}
+
+func TestActiveToolNamesForTurn(t *testing.T) {
 	t.Parallel()
 
 	makeTools := func(names ...string) []fantasy.AgentTool {
@@ -70,10 +138,33 @@ func TestAllowedPlanToolNames(t *testing.T) {
 		return tools
 	}
 
-	t.Run("RootPlanModeIncludesOnlyAllowlistedBuiltIns", func(t *testing.T) {
+	planMode := database.NullChatPlanMode{
+		ChatPlanMode: database.ChatPlanModePlan,
+		Valid:        true,
+	}
+
+	t.Run("NormalModeReturnsAllRegisteredTools", func(t *testing.T) {
 		t.Parallel()
 
-		got := allowedPlanToolNames(makeTools(
+		got := activeToolNamesForTurn(makeTools(
+			"read_file",
+			"propose_plan",
+			"custom_tool",
+			"execute",
+		), database.NullChatPlanMode{}, uuid.NullUUID{}, nil)
+
+		require.Equal(t, []string{
+			"read_file",
+			"propose_plan",
+			"custom_tool",
+			"execute",
+		}, got)
+	})
+
+	t.Run("PlanModeIncludesOnlyAllowlistedBuiltIns", func(t *testing.T) {
+		t.Parallel()
+
+		got := activeToolNamesForTurn(makeTools(
 			"read_file",
 			"write_file",
 			"edit_files",
@@ -95,7 +186,7 @@ func TestAllowedPlanToolNames(t *testing.T) {
 			"read_skill",
 			"read_skill_file",
 			"ask_user_question",
-		), uuid.NullUUID{})
+		), planMode, uuid.NullUUID{}, nil)
 
 		require.Equal(t, []string{
 			"read_file",
@@ -117,10 +208,10 @@ func TestAllowedPlanToolNames(t *testing.T) {
 		}, got)
 	})
 
-	t.Run("ChildPlanModeAllowsExplorationOnly", func(t *testing.T) {
+	t.Run("PlanModeChildChatsAllowExplorationOnly", func(t *testing.T) {
 		t.Parallel()
 
-		got := allowedPlanToolNames(makeTools(
+		got := activeToolNamesForTurn(makeTools(
 			"read_file",
 			"write_file",
 			"edit_files",
@@ -137,7 +228,7 @@ func TestAllowedPlanToolNames(t *testing.T) {
 			"read_skill",
 			"read_skill_file",
 			"ask_user_question",
-		), uuid.NullUUID{UUID: uuid.New(), Valid: true})
+		), planMode, uuid.NullUUID{UUID: uuid.New(), Valid: true}, nil)
 
 		require.Equal(t, []string{
 			"read_file",
@@ -146,6 +237,67 @@ func TestAllowedPlanToolNames(t *testing.T) {
 			"read_skill",
 			"read_skill_file",
 		}, got)
+		require.NotContains(t, got, "write_file")
+		require.NotContains(t, got, "edit_files")
+		require.NotContains(t, got, "ask_user_question")
+		require.NotContains(t, got, "propose_plan")
+		require.NotContains(t, got, "spawn_explore_agent")
+	})
+
+	t.Run("PlanModeStillExcludesDangerousTools", func(t *testing.T) {
+		t.Parallel()
+
+		got := activeToolNamesForTurn(makeTools(
+			"execute",
+			"process_output",
+			"message_agent",
+			"spawn_computer_use_agent",
+			"propose_plan",
+		), planMode, uuid.NullUUID{}, nil)
+
+		require.Equal(t, []string{"execute", "process_output", "propose_plan"}, got)
+		require.NotContains(t, got, "message_agent")
+		require.NotContains(t, got, "spawn_computer_use_agent")
+	})
+
+	t.Run("PlanModeExcludesUnknownTools", func(t *testing.T) {
+		t.Parallel()
+
+		got := activeToolNamesForTurn(makeTools(
+			"read_file",
+			"custom_tool",
+			"another_custom_tool",
+			"propose_plan",
+		), planMode, uuid.NullUUID{}, nil)
+
+		require.Equal(t, []string{
+			"read_file",
+			"propose_plan",
+		}, got)
+		require.NotContains(t, got, "custom_tool")
+		require.NotContains(t, got, "another_custom_tool")
+	})
+
+	t.Run("PlanModeIncludesOnlyApprovedExternalMCPTools", func(t *testing.T) {
+		t.Parallel()
+
+		approvedConfigID := uuid.New()
+		blockedConfigID := uuid.New()
+		got := activeToolNamesForTurn([]fantasy.AgentTool{
+			newTestAgentTool("read_file"),
+			newTestMCPAgentTool("approved-mcp__echo", approvedConfigID),
+			newTestMCPAgentTool("blocked-mcp__echo", blockedConfigID),
+			newTestAgentTool("workspace-mcp__echo"),
+		}, planMode, uuid.NullUUID{}, map[uuid.UUID]struct{}{
+			approvedConfigID: {},
+		})
+
+		require.Equal(t, []string{
+			"read_file",
+			"approved-mcp__echo",
+		}, got)
+		require.NotContains(t, got, "blocked-mcp__echo")
+		require.NotContains(t, got, "workspace-mcp__echo")
 	})
 }
 
@@ -197,10 +349,6 @@ func TestAllowedBehaviorToolNames(t *testing.T) {
 	}
 
 	allTools := makeTools("read_file", "custom_tool", "spawn_explore_agent")
-	planMode := database.NullChatPlanMode{
-		ChatPlanMode: database.ChatPlanModePlan,
-		Valid:        true,
-	}
 	exploreMode := database.NullChatMode{
 		ChatMode: database.ChatModeExplore,
 		Valid:    true,
@@ -210,19 +358,7 @@ func TestAllowedBehaviorToolNames(t *testing.T) {
 		t.Parallel()
 		require.Equal(t, []string{"read_file", "custom_tool", "spawn_explore_agent"}, allowedBehaviorToolNames(
 			allTools,
-			database.NullChatPlanMode{},
 			database.NullChatMode{},
-			uuid.NullUUID{},
-		))
-	})
-
-	t.Run("PlanModeUsesPlanAllowlist", func(t *testing.T) {
-		t.Parallel()
-		require.Equal(t, []string{"read_file", "spawn_explore_agent"}, allowedBehaviorToolNames(
-			allTools,
-			planMode,
-			database.NullChatMode{},
-			uuid.NullUUID{},
 		))
 	})
 
@@ -230,13 +366,40 @@ func TestAllowedBehaviorToolNames(t *testing.T) {
 		t.Parallel()
 		require.Equal(t, []string{"read_file"}, allowedBehaviorToolNames(
 			allTools,
-			database.NullChatPlanMode{},
 			exploreMode,
-			uuid.NullUUID{UUID: uuid.New(), Valid: true},
 		))
 	})
 }
 
+func TestStopAfterPlanTools(t *testing.T) {
+	t.Parallel()
+
+	planMode := database.NullChatPlanMode{
+		ChatPlanMode: database.ChatPlanModePlan,
+		Valid:        true,
+	}
+
+	t.Run("NormalModeReturnsNil", func(t *testing.T) {
+		t.Parallel()
+		require.Nil(t, stopAfterPlanTools(database.NullChatPlanMode{}, uuid.NullUUID{}))
+	})
+
+	t.Run("RootPlanModeIncludesClarificationTool", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, map[string]struct{}{
+			"propose_plan":      {},
+			"ask_user_question": {},
+		}, stopAfterPlanTools(planMode, uuid.NullUUID{}))
+	})
+
+	t.Run("ChildPlanModeSkipsClarificationTool", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, map[string]struct{}{
+			"propose_plan": {},
+		}, stopAfterPlanTools(planMode, uuid.NullUUID{UUID: uuid.New(), Valid: true}))
+	})
+}
+
 func TestStopAfterBehaviorTools(t *testing.T) {
 	t.Parallel()
 

coderd/x/chatd/chatd_test.go

@@ -379,6 +379,37 @@ func TestPlanModeSubagentChatExcludesAskUserQuestion(t *testing.T) {
 
 	_ = agenttest.New(t, client.URL, agentToken)
 
+	// Start an external MCP server whose tools should remain available to the
+	// root plan-mode chat but stay hidden from plan-mode subagents.
+	mcpSrv := mcpserver.NewMCPServer("plan-root-mcp", "1.0.0")
+	mcpSrv.AddTools(mcpserver.ServerTool{
+		Tool: mcpgo.NewTool("echo",
+			mcpgo.WithDescription("Echoes the input"),
+			mcpgo.WithString("input",
+				mcpgo.Description("The input string"),
+				mcpgo.Required(),
+			),
+		),
+		Handler: func(_ context.Context, req mcpgo.CallToolRequest) (*mcpgo.CallToolResult, error) {
+			input, _ := req.GetArguments()["input"].(string)
+			return mcpgo.NewToolResultText("echo: " + input), nil
+		},
+	})
+	mcpTS := httptest.NewServer(mcpserver.NewStreamableHTTPServer(mcpSrv))
+	t.Cleanup(mcpTS.Close)
+
+	mcpConfig, err := client.CreateMCPServerConfig(ctx, codersdk.CreateMCPServerConfigRequest{
+		DisplayName:     "Plan Root MCP",
+		Slug:            "plan-root-mcp",
+		Transport:       "streamable_http",
+		URL:             mcpTS.URL,
+		AuthType:        "none",
+		Availability:    "default_off",
+		Enabled:         true,
+		AllowInPlanMode: true,
+	})
+	require.NoError(t, err)
+
 	var toolsMu sync.Mutex
 	toolsByCall := make([][]string, 0, 2)
 	requestsByCall := make([]recordedOpenAIRequest, 0, 2)
@@ -408,7 +439,7 @@ func TestPlanModeSubagentChatExcludesAskUserQuestion(t *testing.T) {
 		)
 	})
 
-	_, err := expClient.CreateChatProvider(ctx, codersdk.CreateChatProviderConfigRequest{
+	_, err = expClient.CreateChatProvider(ctx, codersdk.CreateChatProviderConfigRequest{
 		Provider: "openai-compat",
 		APIKey:   "test-api-key",
 		BaseURL:  openAIURL,
@@ -428,6 +459,7 @@ func TestPlanModeSubagentChatExcludesAskUserQuestion(t *testing.T) {
 	chat, err := expClient.CreateChat(ctx, codersdk.CreateChatRequest{
 		OrganizationID: user.OrganizationID,
 		PlanMode:       codersdk.ChatPlanModePlan,
+		MCPServerIDs:   []uuid.UUID{mcpConfig.ID},
 		Content: []codersdk.ChatInputPart{
 			{
 				Type: codersdk.ChatInputPartTypeText,
@@ -486,6 +518,8 @@ func TestPlanModeSubagentChatExcludesAskUserQuestion(t *testing.T) {
 		"root plan-mode chat should have execute")
 	require.Contains(t, rootCalls[0], "process_output",
 		"root plan-mode chat should have process_output")
+	require.Contains(t, rootCalls[0], "plan-root-mcp__echo",
+		"root plan-mode chat should have approved external MCP tools")
 	require.NotContains(t, childCalls[0], "ask_user_question",
 		"plan-mode subagent should NOT have ask_user_question")
 	require.NotContains(t, childCalls[0], "write_file",
@@ -496,6 +530,8 @@ func TestPlanModeSubagentChatExcludesAskUserQuestion(t *testing.T) {
 		"plan-mode subagent should have execute")
 	require.Contains(t, childCalls[0], "process_output",
 		"plan-mode subagent should have process_output")
+	require.NotContains(t, childCalls[0], "plan-root-mcp__echo",
+		"plan-mode subagent should NOT have external MCP tools")
 	require.True(t, requestHasSystemSubstring(rootRequests[0], "You are in Plan Mode."))
 	require.True(t, requestHasSystemSubstring(childRequests[0], "You are in Plan Mode as a delegated sub-agent."))
 	require.False(t, requestHasSystemSubstring(childRequests[0], "When the plan is ready, call propose_plan"))
@@ -663,6 +699,227 @@ func TestExploreSubagentIsReadOnly(t *testing.T) {
 	require.Len(t, exploreChildren, 1)
 }
 
+func TestPlanModeRootChatAllowsApprovedExternalMCPTools(t *testing.T) {
+	t.Parallel()
+
+	db, ps := dbtestutil.NewDB(t)
+	ctx := testutil.Context(t, testutil.WaitLong)
+
+	echoMCP := mcpserver.NewMCPServer("plan-visibility-echo", "1.0.0")
+	echoMCP.AddTools(mcpserver.ServerTool{
+		Tool: mcpgo.NewTool("echo",
+			mcpgo.WithDescription("Echoes the input"),
+			mcpgo.WithString("input",
+				mcpgo.Description("The input string"),
+				mcpgo.Required(),
+			),
+		),
+		Handler: func(_ context.Context, req mcpgo.CallToolRequest) (*mcpgo.CallToolResult, error) {
+			input, _ := req.GetArguments()["input"].(string)
+			return mcpgo.NewToolResultText("echo: " + input), nil
+		},
+	})
+	echoTS := httptest.NewServer(mcpserver.NewStreamableHTTPServer(echoMCP))
+	t.Cleanup(echoTS.Close)
+
+	filteredMCP := mcpserver.NewMCPServer("plan-visibility-filtered", "1.0.0")
+	filteredMCP.AddTools(
+		mcpserver.ServerTool{
+			Tool: mcpgo.NewTool("visible",
+				mcpgo.WithDescription("Visible tool"),
+				mcpgo.WithString("input",
+					mcpgo.Description("The input string"),
+					mcpgo.Required(),
+				),
+			),
+			Handler: func(_ context.Context, req mcpgo.CallToolRequest) (*mcpgo.CallToolResult, error) {
+				input, _ := req.GetArguments()["input"].(string)
+				return mcpgo.NewToolResultText("visible: " + input), nil
+			},
+		},
+		mcpserver.ServerTool{
+			Tool: mcpgo.NewTool("hidden",
+				mcpgo.WithDescription("Hidden tool"),
+				mcpgo.WithString("input",
+					mcpgo.Description("The input string"),
+					mcpgo.Required(),
+				),
+			),
+			Handler: func(_ context.Context, req mcpgo.CallToolRequest) (*mcpgo.CallToolResult, error) {
+				input, _ := req.GetArguments()["input"].(string)
+				return mcpgo.NewToolResultText("hidden: " + input), nil
+			},
+		},
+	)
+	filteredTS := httptest.NewServer(mcpserver.NewStreamableHTTPServer(filteredMCP))
+	t.Cleanup(filteredTS.Close)
+
+	var (
+		requests   []recordedOpenAIRequest
+		requestsMu sync.Mutex
+	)
+	openAIURL := chattest.NewOpenAI(t, func(req *chattest.OpenAIRequest) chattest.OpenAIResponse {
+		if !req.Stream {
+			return chattest.OpenAINonStreamingResponse("title")
+		}
+
+		requestsMu.Lock()
+		requests = append(requests, recordOpenAIRequest(req))
+		requestsMu.Unlock()
+
+		return chattest.OpenAIStreamingResponse(
+			chattest.OpenAITextChunks("Done.")...,
+		)
+	})
+
+	user, org, model := seedChatDependenciesWithProvider(ctx, t, db, "openai-compat", openAIURL)
+
+	approvedConfig, err := db.InsertMCPServerConfig(ctx, database.InsertMCPServerConfigParams{
+		DisplayName:     "Plan Approved MCP",
+		Slug:            "plan-approved-mcp",
+		Url:             echoTS.URL,
+		Transport:       "streamable_http",
+		AuthType:        "none",
+		Availability:    "default_off",
+		Enabled:         true,
+		AllowInPlanMode: true,
+		ToolAllowList:   []string{},
+		ToolDenyList:    []string{},
+		CreatedBy:       user.ID,
+		UpdatedBy:       user.ID,
+	})
+	require.NoError(t, err)
+
+	blockedConfig, err := db.InsertMCPServerConfig(ctx, database.InsertMCPServerConfigParams{
+		DisplayName:     "Plan Blocked MCP",
+		Slug:            "plan-blocked-mcp",
+		Url:             echoTS.URL,
+		Transport:       "streamable_http",
+		AuthType:        "none",
+		Availability:    "default_off",
+		Enabled:         true,
+		AllowInPlanMode: false,
+		ToolAllowList:   []string{},
+		ToolDenyList:    []string{},
+		CreatedBy:       user.ID,
+		UpdatedBy:       user.ID,
+	})
+	require.NoError(t, err)
+
+	filteredConfig, err := db.InsertMCPServerConfig(ctx, database.InsertMCPServerConfigParams{
+		DisplayName:     "Plan Filtered MCP",
+		Slug:            "plan-filtered-mcp",
+		Url:             filteredTS.URL,
+		Transport:       "streamable_http",
+		AuthType:        "none",
+		Availability:    "default_off",
+		Enabled:         true,
+		AllowInPlanMode: true,
+		ToolAllowList:   []string{"visible"},
+		ToolDenyList:    []string{},
+		CreatedBy:       user.ID,
+		UpdatedBy:       user.ID,
+	})
+	require.NoError(t, err)
+
+	ws, dbAgent := seedWorkspaceWithAgent(t, db, user.ID)
+	ctrl := gomock.NewController(t)
+	mockConn := agentconnmock.NewMockAgentConn(ctrl)
+	mockConn.EXPECT().SetExtraHeaders(gomock.Any()).AnyTimes()
+	mockConn.EXPECT().ContextConfig(gomock.Any()).
+		Return(workspacesdk.ContextConfigResponse{}, xerrors.New("not supported")).AnyTimes()
+	workspaceToolName := "workspace-plan-mcp__echo"
+	mockConn.EXPECT().ListMCPTools(gomock.Any()).
+		Return(workspacesdk.ListMCPToolsResponse{Tools: []workspacesdk.MCPToolInfo{{
+			ServerName:  "workspace-plan-mcp",
+			Name:        workspaceToolName,
+			Description: "Workspace echo tool",
+			Schema: map[string]any{
+				"input": map[string]any{"type": "string"},
+			},
+			Required: []string{"input"},
+		}}}, nil).
+		Times(1)
+	mockConn.EXPECT().LS(gomock.Any(), gomock.Any(), gomock.Any()).
+		Return(workspacesdk.LSResponse{AbsolutePathString: "/home/coder"}, nil).AnyTimes()
+	mockConn.EXPECT().ReadFile(gomock.Any(), gomock.Any(), gomock.Any(), gomock.Any()).
+		Return(io.NopCloser(strings.NewReader("")), "", nil).AnyTimes()
+
+	server := newActiveTestServer(t, db, ps, func(cfg *chatd.Config) {
+		cfg.AgentConn = func(_ context.Context, agentID uuid.UUID) (workspacesdk.AgentConn, func(), error) {
+			require.Equal(t, dbAgent.ID, agentID)
+			return mockConn, func() {}, nil
+		}
+	})
+
+	planChat, err := server.CreateChat(ctx, chatd.CreateOptions{
+		OrganizationID: org.ID,
+		OwnerID:        user.ID,
+		Title:          "plan-mode-root-mcp-visibility",
+		ModelConfigID:  model.ID,
+		WorkspaceID:    uuid.NullUUID{UUID: ws.ID, Valid: true},
+		PlanMode:       database.NullChatPlanMode{ChatPlanMode: database.ChatPlanModePlan, Valid: true},
+		MCPServerIDs:   []uuid.UUID{approvedConfig.ID, blockedConfig.ID, filteredConfig.ID},
+		InitialUserContent: []codersdk.ChatMessagePart{
+			codersdk.ChatMessageText("List the available tools in plan mode."),
+		},
+	})
+	require.NoError(t, err)
+	waitForChatProcessed(ctx, t, db, planChat.ID, server)
+
+	planChatResult, err := db.GetChatByID(ctx, planChat.ID)
+	require.NoError(t, err)
+	require.Equal(t, database.ChatStatusWaiting, planChatResult.Status)
+
+	askChat, err := server.CreateChat(ctx, chatd.CreateOptions{
+		OrganizationID: org.ID,
+		OwnerID:        user.ID,
+		Title:          "ask-mode-root-mcp-visibility",
+		ModelConfigID:  model.ID,
+		WorkspaceID:    uuid.NullUUID{UUID: ws.ID, Valid: true},
+		MCPServerIDs:   []uuid.UUID{approvedConfig.ID, blockedConfig.ID, filteredConfig.ID},
+		InitialUserContent: []codersdk.ChatMessagePart{
+			codersdk.ChatMessageText("List the available tools outside plan mode."),
+		},
+	})
+	require.NoError(t, err)
+	waitForChatProcessed(ctx, t, db, askChat.ID, server)
+
+	askChatResult, err := db.GetChatByID(ctx, askChat.ID)
+	require.NoError(t, err)
+	require.Equal(t, database.ChatStatusWaiting, askChatResult.Status)
+
+	requestsMu.Lock()
+	recorded := append([]recordedOpenAIRequest(nil), requests...)
+	requestsMu.Unlock()
+	require.Len(t, recorded, 2, "expected exactly one streamed model call per chat")
+
+	planTools := recorded[0].Tools
+	askTools := recorded[1].Tools
+
+	require.Contains(t, planTools, "plan-approved-mcp__echo",
+		"root plan mode should expose approved external MCP tools")
+	require.NotContains(t, planTools, "plan-blocked-mcp__echo",
+		"root plan mode should hide unapproved external MCP tools")
+	require.Contains(t, planTools, "plan-filtered-mcp__visible",
+		"root plan mode should keep allowlisted tools from approved MCP servers")
+	require.NotContains(t, planTools, "plan-filtered-mcp__hidden",
+		"root plan mode should still respect MCP tool allowlists")
+	require.NotContains(t, planTools, workspaceToolName,
+		"root plan mode should exclude workspace MCP tools")
+
+	require.Contains(t, askTools, "plan-approved-mcp__echo",
+		"ask mode should keep approved external MCP tools")
+	require.Contains(t, askTools, "plan-blocked-mcp__echo",
+		"ask mode should keep unapproved-for-plan external MCP tools")
+	require.Contains(t, askTools, "plan-filtered-mcp__visible",
+		"ask mode should keep allowlisted tools from external MCP servers")
+	require.NotContains(t, askTools, "plan-filtered-mcp__hidden",
+		"ask mode should continue respecting MCP tool allowlists")
+	require.Contains(t, askTools, workspaceToolName,
+		"ask mode should continue exposing workspace MCP tools")
+}
+
 func TestInterruptChatClearsWorkerInDatabase(t *testing.T) {
 	t.Parallel()
 
@@ -1151,6 +1408,8 @@ func TestPlanTurnPromptContract(t *testing.T) {
 	require.True(t, requestHasSystemSubstring(recorded[0], "You are in Plan Mode."))
 	require.True(t, requestHasSystemSubstring(recorded[0], "The only intentional authored workspace artifact is the plan file"))
 	require.True(t, requestHasSystemSubstring(recorded[0], "You may use execute and process_output for exploration"))
+	require.True(t, requestHasSystemSubstring(recorded[0], "approved external MCP tools when available"))
+	require.True(t, requestHasSystemSubstring(recorded[0], "Workspace MCP tools are not available in root plan mode"))
 	require.True(t, requestHasSystemSubstring(recorded[0], "After a successful propose_plan call, stop immediately"))
 	require.True(t, requestHasSystemSubstring(recorded[0], planModeInstructions))
 	for _, msg := range recorded[0].Messages {
@@ -5971,6 +6230,286 @@ func TestMCPServerToolInvocation(t *testing.T) {
 		"MCP tool result should be persisted as a tool message in the database")
 }
 
+func TestPlanModeRootChatApprovedExternalMCPToolInvocation(t *testing.T) {
+	t.Parallel()
+
+	db, ps := dbtestutil.NewDB(t)
+	ctx := testutil.Context(t, testutil.WaitLong)
+
+	mcpSrv := mcpserver.NewMCPServer("plan-mode-mcp", "1.0.0")
+	mcpSrv.AddTools(mcpserver.ServerTool{
+		Tool: mcpgo.NewTool("echo",
+			mcpgo.WithDescription("Echoes the input"),
+			mcpgo.WithString("input",
+				mcpgo.Description("The input string"),
+				mcpgo.Required(),
+			),
+		),
+		Handler: func(_ context.Context, req mcpgo.CallToolRequest) (*mcpgo.CallToolResult, error) {
+			input, _ := req.GetArguments()["input"].(string)
+			return mcpgo.NewToolResultText("echo: " + input), nil
+		},
+	})
+	mcpTS := httptest.NewServer(mcpserver.NewStreamableHTTPServer(mcpSrv))
+	t.Cleanup(mcpTS.Close)
+
+	var (
+		callCount      atomic.Int32
+		llmToolNames   []string
+		llmToolsMu     sync.Mutex
+		foundMCPResult atomic.Bool
+	)
+
+	openAIURL := chattest.NewOpenAI(t, func(req *chattest.OpenAIRequest) chattest.OpenAIResponse {
+		if !req.Stream {
+			return chattest.OpenAINonStreamingResponse("title")
+		}
+
+		if callCount.Add(1) == 1 {
+			names := make([]string, 0, len(req.Tools))
+			for _, tool := range req.Tools {
+				names = append(names, tool.Function.Name)
+			}
+			llmToolsMu.Lock()
+			llmToolNames = names
+			llmToolsMu.Unlock()
+
+			return chattest.OpenAIStreamingResponse(
+				chattest.OpenAIToolCallChunk(
+					"plan-mode-mcp__echo",
+					`{"input":"hello from root plan mode"}`,
+				),
+			)
+		}
+
+		for _, msg := range req.Messages {
+			if msg.Role == "tool" && strings.Contains(msg.Content, "echo: hello from root plan mode") {
+				foundMCPResult.Store(true)
+			}
+		}
+
+		return chattest.OpenAIStreamingResponse(
+			chattest.OpenAITextChunks("Planning complete.")...,
+		)
+	})
+
+	user, org, model := seedChatDependenciesWithProvider(ctx, t, db, "openai-compat", openAIURL)
+
+	mcpConfig, err := db.InsertMCPServerConfig(ctx, database.InsertMCPServerConfigParams{
+		DisplayName:     "Plan Mode MCP",
+		Slug:            "plan-mode-mcp",
+		Url:             mcpTS.URL,
+		Transport:       "streamable_http",
+		AuthType:        "none",
+		Availability:    "default_off",
+		Enabled:         true,
+		AllowInPlanMode: true,
+		ToolAllowList:   []string{},
+		ToolDenyList:    []string{},
+		CreatedBy:       user.ID,
+		UpdatedBy:       user.ID,
+	})
+	require.NoError(t, err)
+
+	server := newActiveTestServer(t, db, ps)
+
+	chat, err := server.CreateChat(ctx, chatd.CreateOptions{
+		OrganizationID: org.ID,
+		OwnerID:        user.ID,
+		Title:          "plan-mode-mcp-invocation",
+		ModelConfigID:  model.ID,
+		PlanMode:       database.NullChatPlanMode{ChatPlanMode: database.ChatPlanModePlan, Valid: true},
+		MCPServerIDs:   []uuid.UUID{mcpConfig.ID},
+		InitialUserContent: []codersdk.ChatMessagePart{
+			codersdk.ChatMessageText("Use the approved MCP tool while planning."),
+		},
+	})
+	require.NoError(t, err)
+	waitForChatProcessed(ctx, t, db, chat.ID, server)
+
+	chatResult, err := db.GetChatByID(ctx, chat.ID)
+	require.NoError(t, err)
+	require.Equal(t, database.ChatStatusWaiting, chatResult.Status)
+
+	llmToolsMu.Lock()
+	recordedNames := append([]string(nil), llmToolNames...)
+	llmToolsMu.Unlock()
+	require.Contains(t, recordedNames, "plan-mode-mcp__echo",
+		"approved external MCP tools should be available in root plan mode")
+	require.True(t, foundMCPResult.Load(),
+		"approved external MCP tool results should feed back into the follow-up plan-mode turn")
+}
+
+func TestPlanModeRootChatApprovedExternalMCPWorkflowCanReachProposePlan(t *testing.T) {
+	t.Parallel()
+
+	db, ps := dbtestutil.NewDB(t)
+	ctx := testutil.Context(t, testutil.WaitLong)
+
+	mcpSrv := mcpserver.NewMCPServer("plan-workflow-mcp", "1.0.0")
+	mcpSrv.AddTools(mcpserver.ServerTool{
+		Tool: mcpgo.NewTool("echo",
+			mcpgo.WithDescription("Echoes the input"),
+			mcpgo.WithString("input",
+				mcpgo.Description("The input string"),
+				mcpgo.Required(),
+			),
+		),
+		Handler: func(_ context.Context, req mcpgo.CallToolRequest) (*mcpgo.CallToolResult, error) {
+			input, _ := req.GetArguments()["input"].(string)
+			return mcpgo.NewToolResultText("echo: " + input), nil
+		},
+	})
+	mcpTS := httptest.NewServer(mcpserver.NewStreamableHTTPServer(mcpSrv))
+	t.Cleanup(mcpTS.Close)
+
+	var (
+		callCount          atomic.Int32
+		llmToolNames       []string
+		llmToolsMu         sync.Mutex
+		sawMCPResult       atomic.Bool
+		proposePlanReached atomic.Bool
+	)
+
+	openAIURL := chattest.NewOpenAI(t, func(req *chattest.OpenAIRequest) chattest.OpenAIResponse {
+		if !req.Stream {
+			return chattest.OpenAINonStreamingResponse("title")
+		}
+
+		switch callCount.Add(1) {
+		case 1:
+			names := make([]string, 0, len(req.Tools))
+			for _, tool := range req.Tools {
+				names = append(names, tool.Function.Name)
+			}
+			llmToolsMu.Lock()
+			llmToolNames = names
+			llmToolsMu.Unlock()
+			return chattest.OpenAIStreamingResponse(
+				chattest.OpenAIToolCallChunk(
+					"plan-workflow-mcp__echo",
+					`{"input":"prepare the plan"}`,
+				),
+			)
+		case 2:
+			for _, msg := range req.Messages {
+				if msg.Role == "tool" && strings.Contains(msg.Content, "echo: prepare the plan") {
+					sawMCPResult.Store(true)
+				}
+			}
+			proposePlanReached.Store(true)
+			return chattest.OpenAIStreamingResponse(
+				chattest.OpenAIToolCallChunk("propose_plan", `{}`),
+			)
+		default:
+			return chattest.OpenAIStreamingResponse(
+				chattest.OpenAITextChunks("should not continue")...,
+			)
+		}
+	})
+
+	user, org, model := seedChatDependenciesWithProvider(ctx, t, db, "openai-compat", openAIURL)
+
+	mcpConfig, err := db.InsertMCPServerConfig(ctx, database.InsertMCPServerConfigParams{
+		DisplayName:     "Plan Workflow MCP",
+		Slug:            "plan-workflow-mcp",
+		Url:             mcpTS.URL,
+		Transport:       "streamable_http",
+		AuthType:        "none",
+		Availability:    "default_off",
+		Enabled:         true,
+		AllowInPlanMode: true,
+		ToolAllowList:   []string{},
+		ToolDenyList:    []string{},
+		CreatedBy:       user.ID,
+		UpdatedBy:       user.ID,
+	})
+	require.NoError(t, err)
+
+	ws, dbAgent := seedWorkspaceWithAgent(t, db, user.ID)
+	ctrl := gomock.NewController(t)
+	mockConn := agentconnmock.NewMockAgentConn(ctrl)
+	mockConn.EXPECT().SetExtraHeaders(gomock.Any()).AnyTimes()
+	mockConn.EXPECT().ContextConfig(gomock.Any()).
+		Return(workspacesdk.ContextConfigResponse{}, xerrors.New("not supported")).AnyTimes()
+	mockConn.EXPECT().LS(gomock.Any(), gomock.Any(), gomock.Any()).
+		Return(workspacesdk.LSResponse{AbsolutePathString: "/home/coder"}, nil).AnyTimes()
+	mockConn.EXPECT().ReadFile(gomock.Any(), gomock.Any(), gomock.Any(), gomock.Any()).
+		DoAndReturn(func(_ context.Context, path string, _, _ int64) (io.ReadCloser, string, error) {
+			if strings.HasSuffix(path, ".md") {
+				return io.NopCloser(strings.NewReader("# Plan\n- Use the approved MCP tool findings.\n")), "", nil
+			}
+			return io.NopCloser(strings.NewReader("")), "", nil
+		}).AnyTimes()
+
+	server := newActiveTestServer(t, db, ps, func(cfg *chatd.Config) {
+		cfg.AgentConn = func(_ context.Context, agentID uuid.UUID) (workspacesdk.AgentConn, func(), error) {
+			require.Equal(t, dbAgent.ID, agentID)
+			return mockConn, func() {}, nil
+		}
+	})
+
+	chat, err := server.CreateChat(ctx, chatd.CreateOptions{
+		OrganizationID: org.ID,
+		OwnerID:        user.ID,
+		Title:          "plan-mode-mcp-propose-plan",
+		ModelConfigID:  model.ID,
+		WorkspaceID:    uuid.NullUUID{UUID: ws.ID, Valid: true},
+		PlanMode:       database.NullChatPlanMode{ChatPlanMode: database.ChatPlanModePlan, Valid: true},
+		MCPServerIDs:   []uuid.UUID{mcpConfig.ID},
+		InitialUserContent: []codersdk.ChatMessagePart{
+			codersdk.ChatMessageText("Use the approved MCP tool, then propose the plan."),
+		},
+	})
+	require.NoError(t, err)
+	waitForChatProcessed(ctx, t, db, chat.ID, server)
+
+	chatResult, err := db.GetChatByID(ctx, chat.ID)
+	require.NoError(t, err)
+	require.Equal(t, database.ChatStatusWaiting, chatResult.Status)
+
+	llmToolsMu.Lock()
+	recordedNames := append([]string(nil), llmToolNames...)
+	llmToolsMu.Unlock()
+	require.Contains(t, recordedNames, "plan-workflow-mcp__echo",
+		"approved external MCP tools should be available in the root plan-mode workflow")
+	require.True(t, sawMCPResult.Load(),
+		"the root plan-mode workflow should feed the approved MCP result into the propose_plan turn")
+	require.True(t, proposePlanReached.Load(),
+		"the root plan-mode workflow should reach propose_plan after using the approved MCP tool")
+	require.Equal(t, int32(2), callCount.Load(),
+		"the workflow should stop immediately after propose_plan succeeds")
+
+	var foundProposePlanResult bool
+	testutil.Eventually(ctx, t, func(ctx context.Context) bool {
+		messages, dbErr := db.GetChatMessagesByChatID(ctx, database.GetChatMessagesByChatIDParams{
+			ChatID:  chat.ID,
+			AfterID: 0,
+		})
+		if dbErr != nil {
+			return false
+		}
+		for _, msg := range messages {
+			if msg.Role != database.ChatMessageRoleTool {
+				continue
+			}
+			parts, parseErr := chatprompt.ParseContent(msg)
+			if parseErr != nil {
+				continue
+			}
+			for _, part := range parts {
+				if part.Type == codersdk.ChatMessagePartTypeToolResult && part.ToolName == "propose_plan" {
+					foundProposePlanResult = true
+					return true
+				}
+			}
+		}
+		return false
+	}, testutil.IntervalFast)
+	require.True(t, foundProposePlanResult,
+		"the root plan-mode workflow should persist a propose_plan tool result")
+}
+
 // TestMCPServerOAuth2TokenRefresh verifies that when a chat uses an
 // MCP server with OAuth2 auth and the stored access token is expired,
 // chatd refreshes the token using the stored refresh_token before

coderd/x/chatd/prompt.go

@@ -110,13 +110,17 @@ You may use execute and process_output for exploration, including cloning reposi
 Do not use Plan Mode to implement the requested changes or intentionally modify project files outside the plan file.
 If no workspace is attached to this chat yet, create and start one with create_workspace and start_workspace before investigating.
 If the plan file already exists, read it first with read_file before replacing or refining it.
-Use read_file, execute, process_output, list_templates, read_template, and spawn_agent to gather context. In Plan Mode, spawn_agent delegation is for investigation and planning support, not code writing or implementation.
+Use read_file, execute, process_output, list_templates, read_template, spawn_agent, and approved external MCP tools when available to gather context. Workspace MCP tools are not available in root plan mode, and side-effecting built-in tools such as process_list, process_signal, message_agent, close_agent, and spawn_computer_use_agent remain unavailable. In Plan Mode, spawn_agent delegation is for investigation and planning support, not code writing or implementation.
 Use write_file to create the plan file and edit_files to refine it.
 Use ask_user_question for structured clarification instead of freeform questions.
 When the plan is ready, call propose_plan with the plan file path.
 After a successful propose_plan call, stop immediately. Do not produce follow-up output.
 ` + defaultSystemPromptPlanPathBlockPlaceholder
 
+// Root plan mode may use approved external MCP tools, but delegated
+// plan-mode subagents stay on the narrower built-in-only boundary
+// because their trust boundary is narrower than the root chat's.
+
 // PlanningSubagentOverlayPrompt contains plan-mode instructions for
 // delegated child chats. Child chats may investigate with shell tools
 // but should return findings to the parent instead of authoring the

codersdk/mcp.go

@@ -64,10 +64,11 @@ type MCPServerConfig struct {
 	// Availability policy set by admin.
 	Availability string `json:"availability"` // "force_on", "default_on", "default_off"
 
-	Enabled     bool      `json:"enabled"`
-	ModelIntent bool      `json:"model_intent"`
-	CreatedAt   time.Time `json:"created_at" format:"date-time"`
-	UpdatedAt   time.Time `json:"updated_at" format:"date-time"`
+	Enabled         bool      `json:"enabled"`
+	ModelIntent     bool      `json:"model_intent"`
+	AllowInPlanMode bool      `json:"allow_in_plan_mode"`
+	CreatedAt       time.Time `json:"created_at" format:"date-time"`
+	UpdatedAt       time.Time `json:"updated_at" format:"date-time"`
 
 	// Per-user state (populated for non-admin requests).
 	AuthConnected bool `json:"auth_connected"`
@@ -96,9 +97,10 @@ type CreateMCPServerConfigRequest struct {
 	ToolAllowList []string `json:"tool_allow_list,omitempty"`
 	ToolDenyList  []string `json:"tool_deny_list,omitempty"`
 
-	Availability string `json:"availability" validate:"required,oneof=force_on default_on default_off"`
-	Enabled      bool   `json:"enabled"`
-	ModelIntent  bool   `json:"model_intent"`
+	Availability    string `json:"availability" validate:"required,oneof=force_on default_on default_off"`
+	Enabled         bool   `json:"enabled"`
+	ModelIntent     bool   `json:"model_intent"`
+	AllowInPlanMode bool   `json:"allow_in_plan_mode"`
 }
 
 // UpdateMCPServerConfigRequest is the request to update an MCP server config.
@@ -124,9 +126,10 @@ type UpdateMCPServerConfigRequest struct {
 	ToolAllowList *[]string `json:"tool_allow_list,omitempty"`
 	ToolDenyList  *[]string `json:"tool_deny_list,omitempty"`
 
-	Availability *string `json:"availability,omitempty" validate:"omitempty,oneof=force_on default_on default_off"`
-	Enabled      *bool   `json:"enabled,omitempty"`
-	ModelIntent  *bool   `json:"model_intent,omitempty"`
+	Availability    *string `json:"availability,omitempty" validate:"omitempty,oneof=force_on default_on default_off"`
+	Enabled         *bool   `json:"enabled,omitempty"`
+	ModelIntent     *bool   `json:"model_intent,omitempty"`
+	AllowInPlanMode *bool   `json:"allow_in_plan_mode,omitempty"`
 }
 
 func (c *Client) MCPServerConfigs(ctx context.Context) ([]MCPServerConfig, error) {

docs/ai-coder/agents/architecture.md

@@ -162,8 +162,10 @@ and cannot create workspaces or spawn further sub-agents.
 active. In that mode, `write_file` and `edit_files` are restricted to the
 chat-specific plan file, while `execute` and `process_output` remain available
 for exploration such as cloning repositories, searching code, and running
-inspection commands. MCP, dynamic, provider-native, and computer-use tools are
-not available.
+inspection commands. Root plan-mode chats may also receive administrator-approved
+external MCP tools. Workspace MCP tools remain unavailable in plan mode, and
+plan-mode sub-agents still do not receive any MCP tools. Dynamic,
+provider-native, and computer-use tools are not available.
 
 ### Orchestration tools
 

site/src/api/typesGenerated.ts

@@ -2790,6 +2790,7 @@ export interface CreateMCPServerConfigRequest {
 	readonly availability: string;
 	readonly enabled: boolean;
 	readonly model_intent: boolean;
+	readonly allow_in_plan_mode: boolean;
 }
 
 // From codersdk/organizations.go
@@ -4461,6 +4462,7 @@ export interface MCPServerConfig {
 	readonly availability: string; // "force_on", "default_on", "default_off"
 	readonly enabled: boolean;
 	readonly model_intent: boolean;
+	readonly allow_in_plan_mode: boolean;
 	readonly created_at: string;
 	readonly updated_at: string;
 	/**
@@ -7796,6 +7798,7 @@ export interface UpdateMCPServerConfigRequest {
 	readonly availability?: string;
 	readonly enabled?: boolean;
 	readonly model_intent?: boolean;
+	readonly allow_in_plan_mode?: boolean;
 }
 
 // From codersdk/notifications.go

site/src/pages/AgentsPage/components/AgentChatInput.stories.tsx

@@ -528,6 +528,7 @@ const makeMCPServer = (
 	availability: overrides.availability ?? "default_on",
 	enabled: overrides.enabled ?? true,
 	model_intent: overrides.model_intent ?? false,
+	allow_in_plan_mode: overrides.allow_in_plan_mode ?? false,
 	created_at: overrides.created_at ?? now,
 	updated_at: overrides.updated_at ?? now,
 	auth_connected: overrides.auth_connected ?? false,

site/src/pages/AgentsPage/components/ChatElements/tools/Tool.stories.tsx

@@ -517,6 +517,7 @@ const sampleMCPServers = [
 		availability: "default_on",
 		enabled: true,
 		model_intent: false,
+		allow_in_plan_mode: false,
 		auth_connected: true,
 		created_at: "2025-01-01T00:00:00Z",
 		updated_at: "2025-01-01T00:00:00Z",

site/src/pages/AgentsPage/components/MCPServerAdminPanel.stories.tsx

@@ -33,6 +33,7 @@ const createServerConfig = (
 	availability: overrides.availability ?? "default_on",
 	enabled: overrides.enabled ?? true,
 	model_intent: overrides.model_intent ?? false,
+	allow_in_plan_mode: overrides.allow_in_plan_mode ?? false,
 	created_at: overrides.created_at ?? now,
 	updated_at: overrides.updated_at ?? now,
 	auth_connected: overrides.auth_connected ?? false,

site/src/pages/AgentsPage/components/MCPServerAdminPanel.tsx

@@ -228,6 +228,7 @@ interface MCPServerFormValues {
 	availability: string;
 	enabled: boolean;
 	modelIntent: boolean;
+	allowInPlanMode: boolean;
 	toolAllowList: string;
 	toolDenyList: string;
 	customHeaders: Array<{ key: string; value: string }>;
@@ -257,6 +258,7 @@ const buildInitialValues = (
 	availability: server?.availability ?? "default_off",
 	enabled: server?.enabled ?? true,
 	modelIntent: server?.model_intent ?? false,
+	allowInPlanMode: server?.allow_in_plan_mode ?? false,
 	toolAllowList: joinList(server?.tool_allow_list),
 	toolDenyList: joinList(server?.tool_deny_list),
 	customHeaders: [],
@@ -311,6 +313,7 @@ const ServerForm: FC<ServerFormProps> = ({
 				availability: values.availability,
 				enabled: values.enabled,
 				model_intent: values.modelIntent,
+				allow_in_plan_mode: values.allowInPlanMode,
 				...(values.authType === "oauth2" && {
 					oauth2_client_id: values.oauth2ClientID.trim(),
 					oauth2_client_secret: effectiveOAuth2Secret,
@@ -778,6 +781,26 @@ const ServerForm: FC<ServerFormProps> = ({
 							disabled={isDisabled}
 						/>
 					</div>
+					<div className="flex items-center justify-between">
+						<div>
+							<Label htmlFor={`${formId}-allow-in-plan-mode`}>
+								Allow all tools from this MCP server in root plan mode
+							</Label>
+							<p className="text-sm text-content-secondary">
+								When enabled, the root plan-mode agent can call these tools
+								during planning. Workspace MCP and plan-mode subagents remain
+								restricted.
+							</p>
+						</div>
+						<Switch
+							id={`${formId}-allow-in-plan-mode`}
+							checked={form.values.allowInPlanMode}
+							onCheckedChange={(v) => {
+								form.setFieldValue("allowInPlanMode", v);
+							}}
+							disabled={isDisabled}
+						/>
+					</div>
 					<div className="grid items-start gap-5 sm:grid-cols-2">
 						{" "}
 						<Field

site/src/pages/AgentsPage/components/MCPServerPicker.stories.tsx

@@ -32,6 +32,7 @@ const createServerConfig = (
 	availability: overrides.availability ?? "default_on",
 	enabled: overrides.enabled ?? true,
 	model_intent: overrides.model_intent ?? false,
+	allow_in_plan_mode: overrides.allow_in_plan_mode ?? false,
 	created_at: overrides.created_at ?? now,
 	updated_at: overrides.updated_at ?? now,
 	auth_connected: overrides.auth_connected ?? false,